In a typical cellular communication network, a set of geographically dispersed base stations provide wireless access to a communications infrastructure. Users with wireless communication devices, or terminals, are able to establish a direct communication link with a suitable base station and then exchange information with other users and/or end systems throughout the communication network.
IP multicast technology provides an efficient packet delivery service for group communications (e.g., one-to-many or many-to-many). The use of IP multicast reduces the bandwidth utilization for group communications. This is especially important for supporting group communications over wireless media, where bandwidth is a scarce resource.
When using IP multicast, a group of recipients is associated with an IP multicast address. A data source addresses and sends a single copy of each IP datagram intended for the group of recipients to the IP multicast group address. The routed network will replicate and forward each datagram as needed to deliver it to the routers interconnecting all of the group members. Specialized IP multicast routing protocols are used to form the delivery trees needed for copying and forwarding multicast datagrams.
IP multicast is a receiver-oriented service, in that receivers join a given multicast group to receive datagrams sent to the corresponding IP multicast group address. End systems and access routers communicate with each other via a group membership protocol, e.g., Internet Group Management Protocol (IGMP), to enable the access router to maintain information on active multicast group membership necessary for building the delivery trees.